Fluid pressure system for obtaining, controlling or correcting micrometric displacements in machine-tools and other apparatus

ABSTRACT

This invention relates to a procedure and installatio to obtain, control and correct micrometric displacements of machine tools or other apparatus, wherein one or more elements which deform under internal pressure are placed between two components of a machine and the micro-displacements obtained are measured against a reference element submitted to the same pressure but, if necessary, positioned outside the machine so that the measuring or control apparatus is not subjected to the disturbing effects of vibrations, noises or other causes.

United States Patent Chancel Sept. 5, 1972 FLUID PRESSURE SYSTEM FOROBTAINING, CONTROLLING OR CORRECTING MICROMETRIC DISPLACEMENTS INMACHINE- TOOLS AND OTHER APPARATUS Marcel Georges Chancel, 218, rueGabriel Peri, Vitry sur Seine, France Filed: Sept. 17, 1969 Appl. No.:858,738

Inventor:

US. Cl ..60/54.5 R, 83/9155, 269/22, 91/433 Int. Cl ..F15b 7/00, FlSb13/14, B23q 3/08 Field of Search ..60/54.5 H, 54.5; 83/9155; 269/22;91/1, 4, 33; 417/44 References Cited UNITED STATES PATENTS 5/1944 Webb..9l/433 1,735,964 11/1929 Eule ..60/54.5 3,295,450 1/ 1967 Schonwald etal ..4l7/44 3,277,791 10/1966 Williams et al. ..91/l 2,800,055 7/ 1957May ..60/54.5 3,333,417 8/1967 Hinde ..60/54.5 H

Primary Examiner-Martin P. Schwadron Assistant Examiner-A. M. ZupcicAtzomey-Brown, Murray, Flick & Peckham ABSTRACT This invention relatesto a procedure and installatio to obtain, control and correctmicrometric displacements of machine tools or other apparatus, whereinone or more elements which deform under internal pressure are placedbetween two components of a machine and the micro-displacements obtainedare measured against a reference element submitted to the same pressurebut, if necessary, positioned outside the machine so that the measuringor control apparatus is not subjected to the disturbing effects ofvibrations, noises or other causes.

3 Claims, 12 Drawing Figures PATENTED SEP 5 i973 SHEET 1 OF 7 Hama m Biie wo wo oZEDw wE mpzmwzww umsmwwmm PATENTED SEP 5 I972 SHEET 2 0F 7FLUKE PRESSURE SYSTEM FOR OBTAINING, CONTROLLING R CORRECTINGMHCROMETRTC DISPLACEMENTS IN MACHINE- TOOLS AND OTHER APPARATUS Certainmachine parts necessitate great precision at the manufacturing stage.

However, machine-tools and other apparatus at present used for suchmanufacture show certain imperfections which make it impossible toachieve the required micrometric precisions.

The main causes of inaccuracies are notably:

Variations in levelling instruments. Movements of earth, foundations andfixings;

Distortions of frameworks through expansions or contractions of thermalorigin, application of heat, or ageing;

Bending due to work stresses or to displacements of certain largemasses;

Working tolerances, collapse of oil films, inaccuracies in the guides;

Tolerances and parasite shifting of positioning control systems (Verniergauges, sprockets, screws, etc.);

Tolerances in ball-bearings or other bearings;

Parasite movements in the slide locking systems;

Wear of tools, sliding parts or other parts;

Inaccurate readings of Vernier gauges, maladroitness of operators;

Variations in lubricant viscosities;

Vibrations.

New remedies are constantly applied to these causes of inaccuracies.Normally these remedies lead to a complication of mechanisms,supplementary constraints on use, etc., whence an increase in the costof the machines and, equally, of their running cost.

It must be emphasized that unsatisfactory results from machines are(except for causes relating to vibrations) generally due to smalldivergencies in position between the place actually occupied by acertain machine component (structural element, pin, tool, tool-holder,part-holder, part, etc.) and the place it ought to occupy.

These divergencies are generally very small, and progress tends toreduce them a little more each day.

Thus, to improve the precision of machines, one must accurately obtain,control, inspect, etc., divergencies or displacements of approximatelythe same value as the divergencies, distortions, tolerances, etc., whichcause inaccuracy; i.e., displacements having (i) a minimum value of theorder of one-tenth micron; (ii) a maximum value of the order ofone-tenth millimeter.

indeed, the first difficulties or uncertainties are encountered withprecisions less than one-tenth millimeter. Overcoming these difficultiesentails complexities of conception or construction, with a consequentincrease in manufacturing or running costs.

Also, the present limit of ambitions, if not the needs, of engineeringis situated around one-tenth micron.

A displacement of extremely small amplitude can easily be obtained byacting with considerable thus easily controllable force on a drivencomponent, which extends, collapses or bends.

This principle is often practised when the users manipulate to determinethe final dimension with the flexion of a machines fixed stop or othersimilar component.

The present invention therefore aims at remedying these drawbacks and tothis end concerns a process to obtain micrometric displacements onprecision machine-tools, wherein at least one element which distortsunder internal pressure is placed between two components of a machineand the distortions obtained between the machine components are verifiedby comparison with an identical deforming element submitted to the samepressure.

The invention also concerns an installation for implementing the processfor controlling micrometric displacements, wherein a pressure generatoris connected to the deforming elements being used and to the referenceelement; the distortions of one of these elements act on a measuringdevice connected to a regulator, which acts on the pressure generator tocorrect the pressure value within the deforming elements in accordancewith the data provided by the measuring device.

The invention also extends to the undermentioned characteristics as wellas their divers possible combinations.

An installation conforming to the invention is shown as anon-restrictive example in the attached drawings, in which:

FIG. 1 is a diagrammatic view of the installation conforming to theinvention;

FIG. 2 represents a method of realizing an installation comprisingcontrol and readjustment components;

FIG. 3 represents another method of realizing installations using someitems as readjustment components;

FIG. 4 also represents a method of realization, using electrical andhydraulic means;

FIGS. 5 and 6 represent a method of realization of deforming elementsgenerating micro-displacements;

FIGS. 7 to 12 represent various methods of application to machines ormachine-tool components.

Reference 1 of the installation illustrated diagrammatically in FIG. 1indicates the deforming element positioned in a specific part of themachine-tool, whilst reference 2 indicates the reference deformingelement permitting inspection of distortion by analogy to deformingelement 1.

These two components are connected up and fed from a pressure generator3.

Measurement and readjustment means, schematized under 4, are influencedby modifications in the volume of reference element 2 and influence ahydraulic regulator or distributor 5 which, acting on a pressuregenerator 3 connected to deforming and reference components 1 and 2,maintains the dimension of these components at the desired value. Themeasuring apparatus 4 may be adjusted so as to alter distortion of thedeforming elements at will.

FIG. 2 represents an initial practical application of an installationnecessary for the implementation of the process defined above. Todescribe this figure, let us imagine a surface grinder equipped withmicro-displacement equipment. The operator wishes to displace part 6 inrelation to tool 7 by, for example, 8 centimeters 3 microns andseven-tenths micron. To do this, he displaces the cursor 8 until thepointer is opposite the division corresponding to this mark on thegraduated, adjusted ruler 9. The fluid under pressure then arrives in areceptacle 10 before being distributed via pipe 11 and nozzle 17 onreference deforming element 2.

The arrival of fluid under pressure is effected as indicated by thearrow F1. The fluid is then directed a. for inspection and readjustmentpurposes, towards a receptacle before being sent via pipe 11 and nozzle17 towards reference deforming element 2; b. towards the pressuregenerator 3.

As deforming elements 1 and 2 are in circuit, they are subjected topressure furnished by generator 3 which multiplies the pressure itreceives from F1, and they expand. Expansion of reference element 2restrains the escape of fluid, notably air, at the orifice of nozzle 17.The pressure then increases in receptacle 10. This pressure hasrepercussions on liquid 12 contained in receptacle 10 aforementioned andthe liquid rises in the flexible duct 13 until ball-float 14 isdisplaced in the body of regulator 15 and uncovers the orifices offlexible pipes 16 connected to pressure generator 3.

Pressure inside the generator is then reduced, fluid escaping into theregulator via regulating noules (formed by the orifices of the flexibleliaison pipes). As the total flow from these nozzles is superior to theflow from feed nozzle 16, the pressure tends to fall in the multiplier.

The slightest fall in pressure in the multiplier is immediatelytransmitted to the deforming elements, which contract; this allows thefluid brought by pipe 1 1 to escape more abundantly via nozzle 17. Thelevel of liquid in pipe 13 automatically falls, ball-float 14 thentotally or partially blocks the regulating nozzles formed by theorifices of pipes 16, and this has the effect of reestablishing in theamplifier thus in the deforming elements the exact pressure desired.

As an example, on the graduated scale, one-tenth of a micron correspondsto a height of liquid of 1 mm.

As a variant, it is possible to produce a ball-float and nozzles suchthat the level stabilizes to within one twotenths of a mm., thusmaintaining the height of the deforming elements to within one twohundredths of a micron.

In fact, the ball-float can be balanced so that when it is raised, itliberates the nozzle exhausts one after the other.

The nozzles are of small diameter, and a rise of the ball-float ofone-tenth of a millimeter suffices to double their delivery.

Only one connection is necessary at P1: (compressed air between 5 and 7kglcm There are practically no movable parts in the whole mechanism.

It can be placed outside the machine, still permitting accurateverification of actual displacement.

According to the method of application illustrated in FIG. 2, thegraduated measure 9 travels with arm 8 supporting regulator 15 and thusenables the operator to take readings easily. To improve reading stillfurther, a sighting-piece 18 with magnifying-glass l9 and, possibly,lighting 20 are foreseen.

Before reaching control nozzle 17, air passing into duct 21 isstabilized at constant pressure, for example by jets 22 of differentsection placed on the control circuit in such a way that the surplus,unused air must, in order to escape, overcome the resistance offered bythe two columns of liquid contained in 23.

The feed pressure is thus perfectly regulated and allows work to be donein a more suitable control pressure range.

The space occupied can be reduced.

As the role of the operator is limited to shifting the scaled measure tothe position corresponding to the desired micro-displacements, risks oferrors or blunders are practically non-existent and the regulating israpidly carried out.

In accordance with the application illustrated in this FIG. 2, amechanical control is foreseen and can be automated or pre-defined, orprogrammed.

Another method of application is shown in FIG. 3. The installationsillustrated in FIGS. 2 and 3 present numerous similarities, particularlyin the positioning of elements distorting the control components; theinstallation shown in FIG. 3 also permits remote control ofdisplacements obtained on the machine itself.

The control and adjustment components illustrated in this figure do notallow the self-adjustment of the desired displacement, but merelymaintain constant the pressure inside the deforming elements.

Supposing the operator wishes to obtain the measurement 0.0573 mm., Le.a displacement of five hundred seventy three tenths of a micron. To doso, he acts in one direction or other upon an electric switch 25 andceases his action when the desired figure appears on the meter 26. Heverifies on the graduated scale of the gauge 27 if the measurement isattained and, if not, makes the necessary correction.

The switch 25 controls a small motor 28 whose revolutions are numberedon a meter 26. This motor, through the transmission gear 29 and nut 30,shifts the assembly of which it forms part and which is simply acounterweight on the threaded arm 31. The balance of the arm, previouslyobtained through the membrane 32 being submitted to the pressurereigning in the multiplier, is upset. The arm dips and pushes heavily onthe control of valve 33 (accelerated ascent) which induces air underpressure to the multiplier. The latter sends the high pressure into thedeforming elements 1 and 2 which expand, with pressure also arriving inthe reservoir 32. The air pressure reigning 32 is equal to that actingon the multiplier. This latter pressure tends to balance the arm 31which no longer acts on valve 33. The air passing into 34 at a weak ratecontinues to make the pressure in the multiplier rise slowly, with theresultant consequences.

The pressure generated in 32 continues to make the arm 31 rise slowlyuntil it enters into contact with the valve 35. This latter isexceedingly sensitive and opens under the slightest stress. Its deliveryto the atmosphere is superior to that of orifice 34. The pressure in themultiplier therefore decreases. But, as soon as this pressure decreases,the arm dips and the valve 35 no longer delivers to the atmosphere. Thepressure increases again via the delivery from 34, and so on.

By these means, then, the arm 31 is stabilized and this unit acts as avery sensitive, self-equilibrating pneumatic balance.

At 36, a distributor permits rapid descentf 37 and 38 are componentswhich act as a shock-absorber.

As can be seen, this pneumatic balance is extremely accurate and permitsthe control of pressures in elements 1 and 2 in such a way thatdistortions therein are extremely feeble in comparison with displacementvalues obtained by machine operators in industry using conventionalmethods.

In FIG. 3, the control components, such as pneumatic gauge, electroniccomparator, etc., are stocked in commerce as standard components ofcurrent supplies.

The system of measuring pneumatically or electronically can in this caseonly cover a small part of the measuring scale with very great accuracy.

This small part of the scale can be controlled classic comparator to thenearest micron.

Finally, automation is complete if switch 25 is controlled by means ofany system in function of results registered by the control component 27(e.g., photo-electn'c cell, electronic gauge, proximity contact, etc.).

A different application is represented in FIG. 4. It presents numerousanalogies with the installations shown in FIGS. 2 and 3.

In the description of the embodiment shown in FIG. 4, all the elementsshown in FIG. 1 are referred to, namely:

the deforming elements under references 1 and 2;

the pressure generator under reference 3;

- the group A under reference 4;

the hydraulic distributor under reference 5, shown as reference 44 insaid FIG. 2.

This application is essentially different from the preceding ones inthat here the pressure generator 3 is a high pressure hydraulic group,and also the control circuit 11 is fed by a liquid and not by compressedair or other gas.

The pressure of the liquid is obtained by its own weight in the columnformed by the feed piping 21.

The upper reservoir 50, at a constant level, feeds piping 11, the exitnozzle of which 17 measures expansions of reference element 2.

This circuit is insensitive to atmospheric pressure variations since allexits are in contact with the ambient atmosphere.

In the same way as in the FIG. 2 installation, the column of liquidrises in the reservoir 15 when pilot element 2 expands.

This raising of the level raises the ball-float 14 which acts on theupper electrical contact 41.

This electrical contact closes the delivery from the hydraulic groupgenerating high pressure, by way of the hydraulic distributor 44.

A small leak is incorporated in 42 so that the pressure in the highpressure circuit lessens gradually, allowing progressive decompressionof the accumulator 47.

Consequently, the deforming elements 1 and 2 contract slowly, and thisincreases the outlet, and hence the delivery at the exit nozzle 17 inpipework l1 and makes the level descend in the reservoir 15.

bya

The ball-float no longer acts on the upper micro-contact 41, and thisenables the hydraulic distributor 44 to return to its mean position andresults in a slow increase in pressure in the hydraulic circuit and inthe deforming elements; in effect, the outflow from the distributor 44in a mean position is greater than that from the leak incorporated in42; for this reason, with the elements swelling under the influence ofpressure, the outlet at 17 decreases, the column of liquid rises in thepiping 11, and so on, in this way keeping the dimensions of thedeforming elements 1 and 2 almost constant.

Like the upper micro-contact, the lower micro-contact 43 of theball-float 14 acts on the distributor 44, and serves to increasepressure rapidly when the group A is displaced a considerable-amountalong its column as required for the desired micro-displacements.

On this circuit also, as moreover on the high pressure circuits of FIGS.2 and 3, a joint 48 can be connected which permits the simultaneous orseparate alimentation of other groups of deforming elements.

A single installation for supervision and readjustment and a singlepressure generator can also serve different purposes and even controlmicro-displacements on several machines.

A manometer 49 can also be connected into the high pressure circuit, toindicate the value of the pressure acting in the deforming elements.

For each variation in pressure there .is a corresponding variation insize of the deforming elements.

For example, if a variation in pressure of 0.2 barslcm corresponds to anexpansion of one-tenth of a micron, the manometer can be calibrated andgraduated in such a way as to indicate in microns or fractions of amicron the micro-displacements obtained by the deforming elements.

The installation described in FIG. 4 is extremely easy to use, since theoperator can obtain the micro-displacement he desires simply bydisplacing the group A on its supporting column and reading the requiredmeasurement on the calibrated rule 9.

The majority of components in this installation are diffused incommerce.

The generator, which in this figure is a hydraulic group, permitsunlimited feeding of any number of components, regardless of theirdimensions.

It can also tolerate some leaks in the high pressure circuit and thuspermits the connecting and disconnecting of the different machines orapparatus which may have to be controlled by the same inspection andreadjustment installation, as it allows feeding of deforming elementsmounted on a part animated by a rotary movement.

For example, broaches or tool-holders.

In this case, these elements are generally fed by means of revolvingjoints or couplings mounted on the piping and these joints rarely haveno leaks, whence the necessity for having at ones disposal both pressureand a delivery.

FIGS. 5 and 6 each represent the deforming element which generatesmicro-displacements: FIG. 5 shows a vertical cross-section seen inelevation, FIG. 6 a crosssection seen from above. This deforming elementis made up of three components:

a main body 39 and two platens 40 which hermetically seal the orificesof the main body 39. This body presents a hollow annular distortion suchthat it lends itself to axial distortions under the effect of internalpressure via elasticity of the area delimited by arrows F2.

Various applications are noted hereafter and illustrated in FIGS. 7 to12. Thus FIG. 7 represents a precision mandrel holding the piece 6 to bemachined.

Other precision mandrels or sine-bars, vices and other fixing systemsfor parts can also be provided with a micro-displacement device.

As with magnetic platens, they then constitute homogeneous, independentunits.

They can be coupled or uncoupled separately from the pressure generatorsand checking components.

In effect, the adjustment checking systems and the pressure generatorscan control alternatively or simultaneously one or several groups suchas mandrels, magnetic platen, poppet-head, loose head, tool-holders,machine components, etc., making use of the connecting joint 48 with oneor several connections.

FIG. 8 shows another application. With this one, magnetic platens,sine-bars, vices, and mandrels can be equipped with deforming elementswhich allow a very slight rotation, or false parallelism, and permitvery accurate rectification of conic plugs or other similar parts.

Among other applications which can be foreseen, and not shown on theattached figures, mention can be made of:

surface grinders in which the deforming elements shown in FIGS. 2, 3 and4 can be included in the engine columns and placed, for example, underthe table or poppet-head pin carrier;

all other grinders or precision machines and amongst others, machines togrind the internal and external casing of cylinders, precision markersand drilling machines, etc., to obtain the desired displacements betweentools and parts to be machined as well as to verify or correct thedistortion of their frameworks;

machines which grind directly from solid or submerged sections in whichthe deforming elements permit continuous correction of wear of thegrinding wheels;

lathes of large dimensions for tool gear correction as well as forobtaining slight convex curves as on papermill cylinders;

sight glasses of lathes or grinders for their alignment at the diameteror vertically;

readjustments of tools in general, out of the machine or whilst it is inoperation, and the extraction of tools at one end of their work passageto avoid their leaving traces on their return journey;

, devices to correct guide screws in machines to rectify screw threadsor other items, as well as in numerically controlled machines, etc.;

all machining tools.

Other applications are also shown in FIGS. 9 and 10 for adaptation ontoa cylindrical grinder.

A micro-displacement device can be included in the support of the feedpoppet-head of the rotating part, as well as in the loose head of acylindrical grinder.

The advantages to be drawn from such an application are equallynumerous:

take-up of wear of the grinding wheel;

take-up of differences in diameter due to regrinding (diamonding);

stoppage of work when the theoretical or actual measurement is attained;

submerged work, etc.

It is equally possible, by controlling the deforming elements includedin the feed poppet-head separately from those in the loose head, toobtain take-up of faults in the alignment of these parts or veryaccurate fine cones.

FIG. 4, shows a machine-tool broach. An annular or toric-shapeddeforming work element 1, or several deforming elements positioned on acircumference, permit the adjustment of the play of a bearing, infunction of its temperature, the loads it bears, the linear expansion ofthe broach, or the accuracy of work demanded. The controlled expansionof this or these elements have a direct influence on the quality andaccuracy of the work carried out by the machine-tool, or on the part,which is supported by the broach.

Finally, FIG. 12 shows a device for blocking slides.

Precision machines, such as markers and grinders, often have tablessliding on bearings, needle points, or shoes with ball circulation. Forthese reasons, it is difficult to block them into position when workrequires it. In effect, attempts at blocking risk deteriorating thecontact surfaces of the bearings themselves.

The deforming elements can be used as shown in FIG. 12.

This is an instance of a less noble application, since there is nolonger any question of micro-displacement.

In this case, the deforming elements function on an all or nothing"basis. The adjustment part of FIGS. 1, 2, 3 and 4 is unnecessary. Allthat is needed is a source of pressure.

Thanks to their small bulk and their great power, the deforming elementscan be included in already-existing machines.

independently of the applications cited heretofore, certain others areequally worthy of retention.

There is a demand in certain other domains, listed below, whereapplications are possible; such as:

control machines and even inspection and measuring apparatus;

surface-plates for inspection and measurement (maintenance of horizontaland vertical planes);

industrial optics (controls and measurements by luminous rays and prismefiects); optic fabrication;

research laboratory, testing machines;

precision shearing machines (blade clearance device);

precision rolling-mills (thin blades, precious metals);

electro-erosion machines;

lasers, etc.

Finally, each time that the presence of an operator beside the machineor component at work is dangerous or distressing; as is the case withnoisy or projecting machinery: sparks, shavings or other materials, andwhen there is radiation, as in atomic industry for example, necessitatethe isolation of the control post.

By using the procedure described above, it is thus possible:

on the one hand, to remedy the majority of geometrical faults andinaccuracies noted on machine-tools or similar objects, and to do sowhilst the machine is at rest or in the course of work;

and, on the other hand, to create and control perfectly micrometricmovements while eliminating the inconveniences of classic mechanisms andconsiderably reducing the causes of errors by operators.

Simplification of the regulating machines and precision apparatus alsohas the advantage of saving a considerable amount of time.

It should be understood that the invention is not limited to theembodiments described and represented above; from these it is possibleto foresee other variations which in no way exceed the scope of theinvention.

What is claimed is:

1. Apparatus for controlling micrometric displacements on precisionmachine-tools, comprising a hollow deformable element adapted to beplaced between two components of a machine, a like hollow deformablereference element, means for generating fluid pressure connected to saidelements for applying internal pressure to them, a measuring devicecontrolled by said reference element, and a pressure regulator for saidpressure generating means, said regulator being controlled by saidmeasuring device to correct the pressure within said deformable elementsin accordance with the data provided by the measuring device, saidmeasuring device including a graduated member, an electric switchconnected with said pressure regulator, and means controlled by saidreference element for operating the switch, said switch-operating meansbeing adjustable along said graduated member.

2. Apparatus according to claim 1, including a movable contact for saidswitch, a liquid reservoir, a float in the reservoir supporting saidcontact, a conduit connected with the reservoir and having an outletadjacent said reference element, and means for supplying liquid to thereservoir, the reference element controlling said conduit outlet andhence the level of the liquid in the reservoir.

3. Apparatus for controlling micrometric displacements on precisionmachine-tools, comprising a hollow deformable element adapted to beplaced between two components of a machine, a like hollow deformablereference element, means for generating fluid pressure connected to saidelements for applying internal pressure to them, a measuring devicecontrolled by said reference element, and a pressure regulator for saidpressure generating means, said regulator being controlled by saidmeasuring device to correct the pressure within said deformable elementsin accordance with the data provided by the measuring device, saidpressure regulator including a three-position valve operated by saidmeasuring device with said valve positions consisting of a normalrestricted passage and a fully open passage and a closed position, andsaid measuring device including an electric switch for operating saidvalve and having a movable contact, a liquid reservoir, a float in thereservoir supporting said contact, a conduit connnected with thereservoir and having an outlet adjacent said reference element, andmeans for supplying liquid to the reservoir, the reference elementcontrolling said conduit outlet and hence the level of the liquid in thereservoir.

1. Apparatus for controlling micrometric displacements on precisionmachine-tools, comprising a hollow deformable element adapted to beplaced between two components of a machine, a like hollow deformablereference element, means for generating fluid pressure connected to saidelements for applying internal pressure to them, a measuring devicecontrolled by said reference element, and a pressure regulator for saidpressure generating means, said regulator being controlled by saidmeasuring device to correct the pressure within said deformable elementsin accordance with the data provided by the measuring device, saidmeasuring device including a graduated member, an electric switchconnected with said pressure regulator, and means controlled by saidreference element for operating the switch, said switchoperating meansbeing adjustable along said graduated member.
 2. Apparatus according toclaim 1, including a movable contact for said switch, a liquidreservoir, a float in the reservoir supporting said contact, a conduitconnected with the reservoir and having an outlet adjacent saidreference element, and means for supplying liquid to the reservoir, thereference element controlling said conduit outlet and hence the level ofthe liquid in the reservoir.
 3. Apparatus for controlling micrometricdisplacements on precision machine-tools, comprising a hollow deformableelement adapted to be placed between two coMponents of a machine, a likehollow deformable reference element, means for generating fluid pressureconnected to said elements for applying internal pressure to them, ameasuring device controlled by said reference element, and a pressureregulator for said pressure generating means, said regulator beingcontrolled by said measuring device to correct the pressure within saiddeformable elements in accordance with the data provided by themeasuring device, said pressure regulator including a three-positionvalve operated by said measuring device with said valve positionsconsisting of a normal restricted passage and a fully open passage and aclosed position, and said measuring device including an electric switchfor operating said valve and having a movable contact, a liquidreservoir, a float in the reservoir supporting said contact, a conduitconnnected with the reservoir and having an outlet adjacent saidreference element, and means for supplying liquid to the reservoir, thereference element controlling said conduit outlet and hence the level ofthe liquid in the reservoir.